Lee C S, Tarbell J M
Department of Chemical Engineering, Pennsylvania State University, University Park 16802, USA.
J Biomech Eng. 1997 Aug;119(3):333-42. doi: 10.1115/1.2796098.
The goal of this study was to determine how vessel compliance (wall motion) and the phase angle between pressure and flow waves (impedance phase angle) affect the wall shear rate distribution in an atherogenic bifurcation geometry under sinusoidal flow conditions. Both rigid and elastic models replicating the human abdominal aortic bifurcation were fabricated and the wall shear rate distribution in the median plane of the bifurcation was determined using the photochronic flow visualization method. In the elastic model, three phase angle conditions were simulated (+12, -17, -61 deg), and the results compared with those obtained in a similar rigid model. The study indicates a very low (magnitude close to zero) and oscillatory wall shear rate zone within 1.5 cm distal to the curvature site on the outer (lateral) wall. In this low shear rate zone, unsteadiness (pulsatility) of the flow greatly reduces the mean (time-averaged) wall shear rate level. Vessel wall motion reduces the wall shear rate amplitude (time-varying component) up to 46 percent depending on the location and phase angle in the model. The mean wall shear rate is less influenced by the wall motion, but is reduced significantly in the low shear region (within 1.5 cm distal to the curvature site on the outer wall), thus rendering the wall shear rate waveform more oscillatory and making the site appear more atherogenic. The effect of the phase angle is most noteworthy on the inner wall close to the flow divider tip where the mean and amplitude of wall shear rate are 31 and 23 percent lower, respectively, at the phase angle of -17 deg than at -61 deg. However, the characteristics of the wall shear rate distribution in the low shear rate zone on the outer wall that are believed to influence localization of atherosclerotic disease, such as the mean wall shear rate level, oscillation in the wall shear rate waveform, and the length of the low and oscillatory wall shear rate zone, are similar for the three phase angles considered. The study also showed a large spatial variation of the phase angle between the wall shear stress waveform and the circumferential stress waveform (hoop stress due to radial artery expansion in response to pressure variations) near the bifurcation (up to 70 deg). The two stresses became more out of phase in the low mean shear rate zone on the outer wall (wall shear stress wave leading hoop stress wave as much as 125 deg at the pressure-flow phase angle of -61 deg) and were significantly influenced by the impedance phase angle.
本研究的目的是确定在正弦流条件下，血管顺应性（管壁运动）以及压力波与血流波之间的相位角（阻抗相位角）如何影响致动脉粥样硬化分叉几何形状中的壁面切应力分布。制作了复制人体腹主动脉分叉的刚性和弹性模型，并使用光时流可视化方法确定分叉中平面的壁面切应力分布。在弹性模型中，模拟了三个相位角条件（+12°、-17°、-61°），并将结果与在类似刚性模型中获得的结果进行比较。研究表明，在外（侧）壁曲率部位远端1.5厘米范围内存在一个极低（幅值接近零）且振荡的壁面切应力区。在这个低切应力区，血流的不稳定（脉动性）极大地降低了平均（时间平均）壁面切应力水平。血管壁运动可使壁面切应力幅值（随时间变化的分量）降低多达46%，这取决于模型中的位置和相位角。平均壁面切应力受血管壁运动的影响较小，但在低切应力区域（在外壁曲率部位远端1.5厘米范围内）显著降低，从而使壁面切应力波形更具振荡性，使该部位看起来更易发生动脉粥样硬化。相位角的影响在靠近分流器尖端的内壁上最为显著，在-17°相位角时，壁面切应力的平均值和幅值分别比-61°相位角时低31%和23%。然而，对于所考虑的三个相位角，在外壁低切应力区壁面切应力分布的特征，如平均壁面切应力水平、壁面切应力波形的振荡以及低振荡壁面切应力区的长度，被认为会影响动脉粥样硬化疾病的定位，它们是相似的。研究还表明，在分叉附近，壁面切应力波形与周向应力波形（由于压力变化导致径向动脉扩张产生的环向应力）之间的相位角存在很大的空间变化（高达70°）。在外壁低平均切应力区，这两种应力的相位差更大（在-61°压力-血流相位角时，壁面切应力波超前环向应力波多达125°），并且受到阻抗相位角的显著影响。
